docs: def gravity(latitude, H):
      r'''Calculates local acceleration due to gravity `g` according to [1]_.
      Uses latitude and height to calculate `g`.
  
      .. math::
          g = 9.780356(1 + 0.0052885\sin^2\phi - 0.0000059^22\phi)
          - 3.086\times 10^{-6} H
  
      Parameters
      ----------
      latitude : float
          Degrees, [degrees]
      H : float
          Height above earth's surface [m]
  
      Returns
      -------
      g : float
          Acceleration due to gravity, [m/s^2]
  
      Notes
      -----
      Better models, such as EGM2008 exist.
  
      Examples
      --------
      >>> gravity(55, 1E4)
      9.784151976863571
  
      References
      ----------
      .. [1] Haynes, W.M., Thomas J. Bruno, and David R. Lide. CRC Handbook of
         Chemistry and Physics. [Boca Raton, FL]: CRC press, 2014.
      '''
      lat = latitude*pi/180
      g = 9.780356*(1+0.0052885*sin(lat)**2 -0.0000059*sin(2*lat)**2)-3.086E-6*H
      return g